CODEWITHSUNDEEP
core-dataconcurrency
cai
cai

Reputation: 11

Core Data and Concurrency, 2 solution, which way shou I use?

I get some data from server and I need to parse it. Then some of the parse result may need to save using core data.

this is my code now:

- (void)receiveSomeMessage:(NSString *)message
{
    [self performSelectorInBackground:@selector(parseMessage:) withObject:message];
}

- (void) parseMessage:(NSString *)message
{
    NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
    NSManagedObjectContext *BGMOC =  [[NSManagedObjectContext alloc] init];
    [BGMOC setPersistentStoreCoordinator:[self.appDelegate persistentStoreCoordinator]];

    //parse it
    //write to core data 

    NSNotificationCenter *dnc = [NSNotificationCenter defaultCenter];
    [dnc addObserver:self selector:@selector(addContextDidSave:)    name:NSManagedObjectContextDidSaveNotification object:BGMOC];

    NSError *saveError;
        if (![BGMOC save:&saveError]) {
            //handle the error
        }
    [dnc removeObserver:self name:NSManagedObjectContextDidSaveNotification object:BGMOC];
}

- (void)addContextDidSave:(NSNotification*)saveNotification {

// Merging changes causes the fetched results controller to update its results
[self.appDelegate.managedObjectContext   mergeChangesFromContextDidSaveNotification:saveNotification];
}

This seems to work.

But Apple's Document says: Saving in a Background Thread is Error-prone.

So i wonder is this work:

-(void) parseMessage:(NSString *)message 

{ NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; 
   //parse it and save it to a dictionary
    [self performSelectorOnMainThread:@selector(saveToCoreData:) withObject:dictionary waitUntilDone:YES];
 [pool release];
}

After parse the message,I packet it into a dictionery and pass it to main thread and do the core data thing there. Does this work? if it works, is it better?

Thanks.

Upvotes: 1

Views: 602

Answers (1)

TechZen
TechZen

Reputation: 64428

The Apple docs don't say that saving in the background is technologically error-prone, they imply that programmers are prone to make errors when saving in the background:

Asynchronous queues and threads do not prevent an application from quitting. (Specifically, all NSThread-based threads are “detached”—see the documentation for pthread for complete details—and a process runs only until all not-detached threads have exited.) If you perform a save operation in a background thread, therefore, it may be killed before it is able to complete. If you need to save on a background thread, you must write additional code such that the main thread prevents the application from quitting until all the save operation is complete.

Translation: "When quitting, the programmer has to pay specific attention to the save state of background operations and, a lot of the time, they don't."

Upvotes: 3

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